The present invention relates generally to a turbine nozzle for a gas turbine engine and, in particular, to the balanced support of leaf seals to an inner band of such turbine nozzle.
It will be appreciated that a nozzle for the high pressure turbine of a gas turbine engine is provided in order to receive the active flowpath gas stream at the exit of the combustor and turn such gas stream to meet the spinning rotor of the high pressure turbine. The turbine nozzle is typically made up of a plurality of segments to form an annulus, where each segment includes an outer band, an inner band, and one or more hollow airfoils positioned therebetween. In order to provide separation between the hot gas stream and a cooling flow located both radially inside and outside of the turbine nozzle, leaf seals have been installed on the inner and outer bands. This has been accomplished more recently by means of loading pins in conjunction with pre-loaded springs, as seen, for example, in U.S. Pat. No. 5,797,723 to Frost et al. In this way, the leaf seals are retained in position without any gap between the leaf seal and nozzle.
While loaded springs have been demonstrated to be an effective solution to the problem of loosely installed seals, it has been found that such leaf seals are not supported in balance due to the configuration of the nozzle and the positioning of the loading pins in a non-symmetrical manner. Accordingly, cantilever loading forces are imposed upon the leaf seals. Under some circumstances, the uneven loading combined with vibration and pressure fluctuation could cause liberation of the leaf seal. It will be appreciated that once the seal liberates, the back flow margin on the leading edge of that particular vane will decrease, causing a weak cooling flow, or even back flow, to the vane. Furthermore, if the broken leaf seal happens to block the insert inlet of the band, and greatly limits the cooling supply, the vane will be under elevated temperature and fail quickly.
Thus, in light of the foregoing, it would be desirable for an improved turbine nozzle design to be developed which provides balanced support of the leaf seals at the inner and outer nozzle bands without affecting performance and reliability of the turbine nozzle. It would also be desirable that minimal changes to the components of existing turbine nozzles be required so that those turbine nozzles in the field may be easily altered to provide the desired support to the leaf seals.
In a first exemplary embodiment of the invention, a segment of an annular band utilized to support a turbine nozzle of a gas turbine engine is disclosed as including a first end and a second end opposite thereof, a flange portion extending between the first and second ends, a second portion extending between the first and second ends opposite the flange portion, a surface extending between the first and second ends and the flange and second portions, wherein at least one inlet is formed therein, at least one lug positioned adjacent the flange portion for receiving a pin to attach a leaf seal to the band segment, and at least one protrusion extending from the surface to assist in providing balanced support to a leaf seal attached to the band segment.
In a second exemplary embodiment of the invention, a turbine nozzle assembly for a gas turbine engine is disclosed as including a plurality of segments joined together to form an outer band, a plurality of segments joined together to form an inner band, at least one airfoil positioned between the outer and inner bands, a leaf seal attached to each inner band segment by at least one pin member, and a leaf seal attached to each outer band segment by at least one pin member. Each inner band segment includes a protrusion extending from a surface thereof so as to provide balanced support to the corresponding leaf seal in conjunction with the pin members. Each of the inner band segments further includes a first portion having a flange extending therefrom, a second portion opposite the first portion, a first end, and a second end opposite the first end, wherein the surface extends between the first and second ends and the first and second portions.